An innovative technique for producing a registered bite image of the teeth in centric occlusion begins with the molding of both the upper and lower teeth using a triple tray. The triple tray is formed from a rigid plastic or preferably metals frame having a lingual and buccal sidewall dam and a thin, porous mesh in the occlusal plane. This mesh is fine enough to allow good occlusion and still act as a support for a quick setting elastomeric compound of polysiloxane or other polymer that solidify to form a resilient rubber mold of the teeth in detail. Triple trays are available for the left or right dental arch and the anterior arch. The triple tray takes three simultaneous impressions of the upper and lower teeth, as well as the bite registration, thus earning its name. As an example, in the right arch, the xe2x80x9cUxe2x80x9d shaped frame is rigid enough to prevent the rubbery impression compound from expanding outward in subsequent casting procedures. This will prevent dimensional inaccuracies in the final restoration. An aluminum or steel frame has the necessary rigidity while occupying little space within the mouth. A convenient handle, preferably detachable, aids in the proper placement of the triple tray.
The triple tray with its embedded and solidified impressions is sent to the dental laboratory for further processing. A set of positive stone casts made from a quick setting plaster are formed within both the upper and lower negative impressions. Registering and attaching these positive stone casts is the subject of this invention. It is desirable that these stone casts are manipulated to mimic the variety of motions of the jaw to provide efficient and comfortable chewing. This is especially necessary when several missing teeth are being restored. The dental practitioner must craft the opposing surfaces while moving the stone casts from side to side and forward and backward matching the dynamic occlusal activity of the jaw. Cusps and fossae are sculpted where necessary to provide the crushing, grinding and cutting action of natural teeth. Often, the dental practitioner or laboratory artisan can improve upon the less than optimal dentition provided by inheritance. The upper and lower casts are held in an articulator in such a manner as to mimic the complex motion of the human jaw. The articulator of choice in this invention consists of a somewhat flexible hinged assembly having a radial opening and closing motion like that of the jaw. In addition the controlled flexing motion of the articulator arms allow the dental practitioner or artisan to manipulate the stone casts by hand. The articulator is provided with removable, adjustable frontal and rear stops.
The current techniques in sophisticated dental laboratories are reliant upon the knowledge and skill of the well trained dental technician to produce prosthetic crowns and bridges that match the opposing dentition. When working with separate casts of the upper and lower arch of the jaw, the technician can often attach the casts to an articulator by visual inspection with good accuracy. In some cases however, the technician must interpolate the desired occlusion. This may be the result of missing or poorly matching teeth. The use of the triple tray gives the technician a tool to replicate prosthetics that best meet the patient""s own sense of his best bite pattern. In this manner the patient is most pleased with the results. However, if the technician should misalign the upper and lower casts by a few microns in cementing them to the jaws of the articulator, the patient will notice the misalignment in the resulting prosthesis.
If one or more teeth being restored are sectioned from the stone cast to allow for easier manipulation while building up the prosthesis, they must be accurately replaced among the other replicas of unaltered teeth in the stone cast. This is often done with alignment or registration pins that are easily slid in and out of matching receptacles formed in a separately cast stone base.
This invention offers refinements in the methods and apparatus by introducing a set pair of opposing articulator pin blocks with repositionable pins. The technician locates the optimal pin position within a block having an array of closely spaced holes. The pins are equipped with heads or a knurled region to hold firmly within the stone cast. The triple tray is first equipped with a confining dam to provide bases for the upper and lower impressions. The plaster slurry is fed into one side of the impression. A vibrating table having a jarring vertical motion, forces the thixotropic slurry to flow into each detail of the mold while driving any entrained bubbles to the top. The first impression block with the pins in place is positioned over the triple tray and locked and registered by means of projections on the dam mating with matching mounting holes in the block. After the plaster has set, the positive stone cast is carefully removed from triple tray impression and the confining dam. The stone cast can be sectioned with a thin saw blade down to the pin block. Each section can be removed and replace by sliding the pins out of and back into the block. The opposing positive stone cast is made using the same procedure by inverting the dam and triple tray assembly and filling the lower plaster recess with plaster slurry.
It is now possible to slide both the upper and lower block into the articulator. The articulator is equipped with an upper and lower frame with slide grooves for receiving the blocks in proper alignment. A detent means with a positive xe2x80x9csnapxe2x80x9d will tell the technician when the blocks are in place. Attracting embedded magnets in both the pin block and articulator jaws can provide good pin block positioning and retention. The articulator has an upper and lower arm attached to the upper and lower frame respectively. The upper and lower arms meet at a hinge that mimics the overall motion of the jaw. At least one of these arms has an elastically flexible element that will allow the two frames to move in lateral and anterior directions to mimic the complex motions of the jaws. When not being manipulated, the articulator frames return to an aligned resting position.
The apparatus of this invention consist of the following elements: A triple tray constructed of a sturdy metal frame and a thin porous membrane mounted on this frame in the occlusal plane known to the art.
A confining rubber dam with an upper and lower plaster casting recess that wraps around the periphery of the triple tray frame and locks into place.
An upper articulator block with a multitude of evenly spaced tapered through-holes, each plugged with a removable rubber plug. The articulator block is made from a transparent, rigid polymer. The plugs are made of a resilient polymer.
A plurality of tapered pins having a tapered base matching the tapered through-holes in the articulator blocks and having a knurled or otherwise machined head to hold the pin within hardened stone.
A lower articulator block and pin set fashioned like the upper block and pins.
The dental technician needs to properly register the occlusal fit between the upper and lower stone casts of at least a section of the teeth. The problem in maintaining this registration as the upper and lower stone casts are attached to an articulator is the subject of this invention.
The dentist takes a triple tray impression of the upper and lower jaw with the teeth held shut in the normal bite position known as centric closure. A single quadrant, left or right or an anterior registration is captured. A full dental arch is also possible. The preferred impression material used is quick setting polymer paste, which sets to a rubbery solid.
Every detail of the dentition and surrounding soft tissue is captured. The triple tray is removed from the patient""s mouth and sent to a lab. The excess rubber compound is trimmed from the surrounding areas of the triple tray, taking care not to disturb the areas of interest.
A prefabricated dam assembly having an upper and a lower pouring recess is fitted around the periphery of the triple tray. The fitting will be liquid tight, but will not distort the triple tray in a manner that would otherwise distort the restoration. This dam assembly has coined hinges that allow the assembly to be folded around the triple tray and locked into position. This confining dam has a partitioning shelf and a pair of upper and lower enclosing walls to form upper and lower recesses for the liquid casting slurry that will harden into a dimensionally accurate upper and lower stone models with mounting bases.
An articulator pin block is prepared with removable tapered pins to match the specific restoration areas. One or more replicated portions of the positive stone cast will be removably attached to the articulator block by means of these tapered pins. The articulator block is equipped with a multitude of equally spaced tapered holes, each sealed with a removable rubber plug. The plugs corresponding to the desired pin positions are punched out leaving an empty tapered hole for each desired pin placement.
The block has mounting and registration means to properly fix it to the top of the walls of the dam. The assembly is thinly coated with a mold release compound to aid in freeing the set stone model from the articulator block and surrounding dam.
A slurry of stone plaster is mixed and degassed according to the manufacturer""s instructions.
The upper pouring recess of the dam and triple tray assembly is filled and bubbles are forced to the top of the recess with a tabletop, impact vibrator.
The prepared articulator block is inverted in the properly keyed location with the pins in place. The stone is allowed to harden. The positive stone cast of the upper rubber dam recess is left in place and the whole assemblage is turned upside down.
Now the lower articulator block with tapered pins inserted is prepared in the same manner as the upper block.
Plaster slurry is carefully ladled and vibrated into the triple tray lower impression and lower dam recess. The lower articulator block with its alignment pins in place is set and keyed into the plaster slurry. After hardening, the lower positive cast and the lower articulator block are removed from the lower triple tray impression and dam assembly.
The upper positive cast and articulator block are removed from the upper impression in the same manner as the lower cast and block.
Now the upper block with the attached positive cast is slipped into the matching groove in the upper articulator arm. The lower block is slipped into its matching groove on the lower articulator arm.
Centric occlusion is preserved since both the upper and lower stone casts were registered to the upper and lower articulator pin blocks during casting and the pin blocks were held in registration with the triple tray and dam assembly by keyed features.